
{
    Uf.oldTime();

    surfaceVectorField nf = mesh.Sf() / mesh.magSf();
    surfaceVectorField Utang = fvc::interpolate( U ) - nf * (fvc::interpolate( U ) & nf);
    surfaceVectorField Unor = phi / mesh.magSf() * nf;

    Uf = Utang + Unor;
}
